Hilary Duff is particpating with the Ad Council and the Gay, Lesbian, and Straight Education Network to encourage people, specially teenagers, to stop using the phrase “That’s So Gay.” In the spot, Hilary observes a pair of teen girls shopping for clothes, with one calling a top “so gay.” Duff tells the girls the phrase is insulting and is heard at the end of the ad telling viewers, “When you say ‘that’s so gay,’ do you realize what you say? Knock it off.” Watch it via YouTube below and check out more details at thinkb4youspeak.com.